Lyophilized Matrix Containing Ready-to-Use Primers and Probe Solution for Standardization of Real-Time PCR and RT-qPCR Diagnostics in Virology

Seroprevalence study in humans and molecular detection in Rhipicephalus sanguineus ticks of severe fever with thrombocytopenia syndrome virus in Thailand

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus with a mortality rate of up to 30%. First identified in China in 2009, it was later reported in other Asian countries, including Thailand in 2020. SFTSV has been detected in several tick species, including Rhipicephalus sanguineus, known for infesting dogs. We conducted a seroprevalence study of SFTSV in Bangkok and Nong Khai, Thailand, by analyzing 1162 human samples collected between 2019 and 2023. The testing method relied on IgG detection using ELISA and confirmed though a virus seroneutralization test. The results indicated that out of the participants, 12 (1.1%) tested positive for anti-SFTSV IgG antibodies; however, none exhibited positive results in the seroneutralization assay. Additionally, molecular detection of SFTSV, Crimean-Congo hemorrhagic fever (CCHF), Coxiella spp., Bartonella spp., and Rickettsia spp. was performed on 433 Rh. sanguineus ticks collected from 49 dogs in 2023 in Chachoengsao Province, Thailand. No evidence of these pathogens was found in ticks. These findings highlight the importance of exploring viral cross-reactivity. Furthermore, it is important to conduct additional studies to isolate SFTSV from animals and ticks in order to identify the potential transmission routes contributing to human and animal infections in Thailand.

Vacuum Oven Drying: A Cost-Effective Way of Producing Field-Deployable Reagents for In-house Real-Time PCR Methods

The polymerase chain reaction (PCR), is a widely used, sensitive and reliable method for detecting pathogens. However, technical limitations may restrict its use outside sophisticated laboratories, e.g. for detecting pathogens at the site of a disease outbreak. In this study, real-time PCR reagents specific to four bacteria (Bacillus anthracis, Yersinia pestis, Francisella tularensis, and Brucella spp.) and to the Influenza A virus were dried using a vacuum oven drying method. The performance of the dried reagents stored at different temperatures, was monitored using both a standard-size and a portable real-time PCR instrument. The vacuum oven dried real-time PCR reagents were stable and retained the sensitivity for at least 14 months when stored in a refrigerator (+ 4 °C). When stored at room temperature, DNA assays remained stable for at least 10 weeks and Influenza A RNA assay for 3 weeks. These results demonstrate the feasibility of vacuum oven dried real-time PCR reagents and a portable thermocycler for the rapid and reliable detection of pathogens. The drying protocol presented here is cost-effective and easy to use, and could be applied to real-time PCR methods specific to other pathogens as well. In addition, this in-house drying protocol reduces reliance on commercial PCR tests during a time of shortage, such as that experienced during the Corovirus disease (COVID-19) crisis.

Evaluation of a novel lyophilized-pellet-based 2019-nCoV nucleic acid detection kit for the diagnosis of COVID-19

The coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has swept the world and poses a serious threat to human health. In the post-pandemic-era, we must remain vigilant against the co-infection of SARS-CoV-2 and other respiratory viruses. More accurate and convenient detection methods are required for the diagnosis of SARS-CoV-2 due to its prolonged existence. In this study, the application value of a novel lyophilized-pellet-based 2019-nCoV nucleic acid diagnostic kit (PCoV-Kit) was evaluated by comparing it with a conventional liquid diagnostic kit (LCoV-Kit). We assessed the sensitivity, precision, accuracy, specificity, and amplification efficiency of PCoV-Kit and LCoV-Kit using diluted SARS-CoV-2 RNA reference materials. The results showed that both kits had high sensitivity, precision, accuracy, and specificity. A total of 2,033 oropharyngeal swab specimens collected during mass screening in Fuzhou in December 2022 were applied for the consistency analysis of the two reagents. In the detection of clinical oropharyngeal swab specimens, although the positive rate of PCoV-Kit (19.28%) was slightly lower than that of LCoV-Kit (20.86%), statistical analysis demonstrated a high degree of consistency between the test results obtained using both kit (χ2 = 1.57, P>0.05; Kappa coefficient = 0.90, 95%CI: 0.88-0.93). In conclusion, the use of lyophilized PCoV-Kit provides a non-inferior assay for the diagnosis of COVID-19.

Diversity and Genetic Reassortment of Keystone Virus in Mosquito Populations in Florida

Keystone orthobunyavirus (KEYV), a member of the genus Orthobunyavirus, was first isolated in 1964 from mosquitoes in Keystone, Florida. Although data on human infections are limited, the virus has been linked to a fever/rash syndrome and, possibly, encephalitis, with early studies suggesting that 20% of persons in the Tampa, Florida, region had antibodies to KEYV. To assess the distribution and diversity of KEYV in other regions of Florida, we collected > 6,000 mosquitoes from 43 sampling sites in St. Johns County between June 2019 and April 2020. Mosquitoes were separated into pools by species and collection date and site. All pools with Aedes spp. (293 pools, 2,171 mosquitoes) were screened with a real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay that identifies KEYV and other closely related virus species of what was previously designated as the California encephalitis serogroup. In 2020, screening for KEYV was expanded to include 211 pools of Culex mosquitoes from sites where KEYV-positive Aedes spp. had been identified. rRT-PCR-positive samples were inoculated into cell cultures, and five KEYV isolates from Aedes atlanticus pools were isolated and sequenced. Analyses of the KEYV large genome segment sequences revealed two distinct KEYV clades, whereas analyses of the medium and small genome segments uncovered past reassortment events. Our data documented the ongoing seasonal circulation of multiple KEYV clades within Ae. atlanticus mosquito populations along the east coast of Florida, highlighting the need for further studies of the impact of this virus on human health.

Evaluation of the performance of a novel HIV-1 viral load assay for HIV quantification in China

OBJECTIVES

Our objective was to assess the HIV-1 quantification performance of the Livzon HIV-1 viral load (VL) assay and the Roche Cobas HIV-1 assay to evaluate an HIV-1 VL testing reagent for application in China.

METHOD

We compared the Livzon and Roche Cobas HIV-1 VL assays using ethylenediaminetetraacetic acid plasma samples collected between May 2021 and November 2021 from patients with HIV-1 and healthy controls. We used Cohen's κ coefficient to measure agreement of qualitative values and Pearson's correlation coefficient (r) values and the coefficient of determination (R² ) to determine the linear relationship between the two assays. We performed a Bland-Altman analysis to assess VL quantification agreement.

RESULTS

In total, 11 plasma samples from patients with hepatitis B virus (HBV) or hepatitis C virus (HCV) and nine samples from healthy controls were undetectable on both assays. Overall agreement was seen in 419 of 500 specimens (91.40%), with a κ value of 0.59. Pearson's correlation coefficient between the two assays was 0.970. Using the Bland-Altman method, 95.14% (352/370) of paired VLs fell within the 95% confidence limits of agreement (-0.51 to 0.95 log₁₀  copies/mL). Higher VLs had a better correlation and a smaller mean difference between the two assays. Pearson's correlation coefficient for the samples of subtype CRF01_AE, CRF07_BC, and CRF55_01B was 0.950, 0.935, and 0.952, respectively.

CONCLUSION

The Livzon HIV-1 VL assay exhibits good precision and linearity and a high correlation with the Roche Cobas HIV-1 assay. The Livzon HIV-1 VL assay has salient advantages in terms of the lyophilized powder reagent, which gives the assay greater stability and sensitivity and can be readily used in low-resource areas.

Genome Sequence of Genotype 1A Hepatovirus A Isolated from Plasma from a Haitian Child

Genotype 1A hepatovirus A was identified by quantitative reverse transcription-PCR and isolated from plasma from a Haitian child with acute undifferentiated febrile illness and malaise. The strain was most closely related to Brazilian strains, consistent with recognized patterns of virus movement in the Caribbean region.

A clinical, aetiological, and public health perspective on central nervous system infections in Bolivia, 2017-2018

Central nervous system (CNS) infections are important causes of morbidity and mortality worldwide. In Bolivia, aetiologies, case fatality, and determinants of outcome are poorly characterised. We attempted to investigate such parameters to guide diagnosis, treatment, prevention, and health policy. From Nov-2017 to Oct-2018, we prospectively enrolled 257 inpatients (20.2% HIV-positive patients) of all ages from healthcare centers of Cochabamba and Santa Cruz, Bolivia with a suspected CNS infection and a lumbar puncture performed. Biological diagnosis included classical microbiology, molecular, serological and immunohistochemical tests. An infectious aetiology was confirmed in 128/257 (49.8%) inpatients, including, notably among confirmed single and co-infections, Cryptococcus spp. (41.7%) and Mycobacterium tuberculosis (27.8%) in HIV-positive patients, and Mycobacterium tuberculosis (26.1%) and Streptococcus pneumoniae (18.5%) in HIV-negative patients. The total mortality rate was high (94/223, 42.1%), including six rabies cases. In multivariate logistic regression analysis, mortality was associated with thrombocytopenia (Odds ratio (OR) 5.40, 95%-CI 2.40-11.83) and hydrocephalus (OR 4.07, 95%-CI 1.35-12.23). The proportion of untreated HIV patients, late presentations of neurotuberculosis, the rate of pneumococcal cases, and rabies patients who did not benefit from a post-exposure prophylaxis, suggest that decreasing the burden of CNS infections requires reinforcing health policy regarding tuberculosis, rabies, S. pneumoniae vaccination, and HIV-infections.

Transferable, easy-to-use and room-temperature-storable PCR mixes for microfluidic molecular diagnostics

As the outbreak of coronavirus disease 2019 (COVID-19), on-site molecular diagnosis is becoming increasingly important. In this study, a freeze-drying method was introduced for PCR reagents to meet the requirements of microfluidic molecular diagnosis. Using this method, PCR components were pre-mixed and freeze-dried as a bead, which could be transferred into microfluidic chips easily. As this bead only required reconstitution in water, operational steps of PCR were simplified, pipetting errors and errors associated with improper handling of wet reagents could also be reduced. In addition, 19 PCR mixes for different targets (including both RNA and DNA) detection were stable when stored at room temperature (18-25 °C) for 1-2 years and may be stored longer as activity monitoring remains ongoing. To shorten the stability testing time, accelerated stability testing at higher temperatures was proposed. The evaluation periods of the freeze-dried PCR mixes were shortened to less than one month when stored at 56 °C and 80 °C. When attempts were further tried to predict the shelf lives for freeze-dried PCR mixes, our findings challenged the classic view of the Q₁₀ method as a prediction model for freeze-dried PCR mixes and confirmed for the first time that this prediction was influenced by different factors at varying degrees. These studies and findings are important for the development of molecular diagnosis at both central laboratories and resource-limited areas.

Lyophilization of premixed COVID-19 diagnostic RT-qPCR reactions enables stable long-term storage at elevated temperature

Reverse transcriptase‐quantitative polymerase chain reaction (RT‐qPCR) diagnostic tests for SARS‐CoV‐2 are the cornerstone of the global testing infrastructure. However, these tests require cold‐chain shipping to distribute, and the labor of skilled technicians to assemble reactions and interpret the results. Strategies to reduce shipping and labor costs at the point‐of‐care could aid in diagnostic testing scale‐up and response to the COVID‐19 outbreak, as well as in future outbreaks.

Lyophilized Ready-to-Use Mix for the Real-Time Polymerase Chain Reaction Diagnosis

Real-time polymerase chain reaction (real-time PCR) brings a more efficient and accurate method for detecting and analyzing nucleic acids in hospitals and laboratories. To solve the inconvenience of PCR reagent delivery and storage via cold-chain transportation, a solid-state reagent with robust characteristics should be employed. In this report, a lyophilized mix containing all necessary components for real-time PCR and its production method was designed, and its stability was tested at different temperatures. Some cryoprotectants and carriers are required to protect the function of the enzyme and primer as much as possible and provide the cake structure. Formulations with polyhydroxy compounds were considered to have the potential for protecting the enzymatic microstructure and functionality of dried mixes during the whole manufacturing and cold-free storage. The final products with the most superior protective formulation containing trehalose, Ficoll 400, and gelatin were able to provide the totally same testing result and sensitivity as the freshly made mix after 300 days of storage at 45 °C and can be deduced to maintain the function at room temperature (22.5-25.5 °C) for about 2 years.

Screening of Additive Formulations Enables Off-Chip Drop Reverse Transcription Quantitative Polymerase Chain Reaction of Single Influenza A Virus Genomes

The miniaturization of polymerase chain reaction (PCR) using drop-based microfluidics allows for amplification of single nucleic acids in aqueous picoliter-sized drops. Accurate data collection during PCR requires that drops remain stable to coalescence during thermocycling and drop contents are retained. Following systematic testing of known PCR additives, we identified an optimized formulation of 1% w/v Tween-20, 0.8 μg/μL bovine serum albumin, 1 M betaine in the aqueous phase, and 3 wt % (w/w) of the polyethylene glycol-perfluoropolyether₂ surfactant in the oil phase of 50 μm diameter drops that maintains drop stability and prevents dye transport. This formulation enables a method we call off-chip drop reverse transcription quantitative PCR (OCD RT-qPCR) in which drops are thermocycled in a qPCR machine and sampled at various cycle numbers "off-chip", or outside of a microfluidic chip. qPCR amplification curves constructed from hundreds of individual drops using OCD RT-qPCR and imaged using epifluorescence microscopy correlate with amplification curves of ≈300,000 drops thermocycled using a qPCR machine. To demonstrate the utility of OCD RT-qPCR, influenza A virus (IAV) RNA was detected down to a single viral genome copy per drop, or 0.320 cpd. This work was extended to perform multiplexed detection of IAV M gene RNA and cellular β-actin DNA in drops, and direct amplification of IAV genomes from infected cells without a separate RNA extraction step. The optimized additive formulation and the OCD-qPCR method allow for drop-based RT-qPCR without complex devices and demonstrate the ability to quantify individual or rare nucleic acid species within drops with minimal processing.

Evaluation of a Trio Toscana Virus Real-Time RT-PCR Assay Targeting Three Genomic Regions within Nucleoprotein Gene

Toscana virus (TOSV) can cause central nervous system infections in both residents of and travelers to Mediterranean countries. Data mining identified three real-time RT-qPCR assays for detecting TOSV RNA targeting non-overlapping regions in the nucleoprotein gene. Here, they were combined to create a multi-region assay named Trio TOSV RT-qPCR consisting of six primers and three probes. In this study, (i) we evaluated in silico the three RT-qPCR assays available in the literature for TOSV detection, (ii) we combined the three systems to create the Trio TOSV RT-qPCR, (iii) we assessed the specificity and sensitivity of the three monoplex assays versus the Trio TOSV RT-qPCR assay, and (iv) we compared the performance of the Trio TOSV RT-qPCR assay with one of the reference monoplex assays on clinical samples. In conclusion, the Trio TOSV RT-qPCR assay performs equally or better than the three monoplex assays; therefore, it provides a robust assay that can be used for both research and diagnostic purposes.

Development and Evaluation of a duo SARS-CoV-2 RT-qPCR Assay Combining Two Assays Approved by the World Health Organization Targeting the Envelope and the RNA-Dependant RNA Polymerase (RdRp) Coding Regions

The recent emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) worldwide has highlighted the importance of reliable and rapid diagnostic testing to prevent and control virus circulation. Dozens of monoplex in-house RT-qPCR assays are already available; however, the development of dual-target assays is suited to avoid false-negative results caused by polymorphisms or point mutations, that can compromise the accuracy of diagnostic and screening tests. In this study, two mono-target assays recommended by WHO (E-Sarbeco (enveloppe gene, Charite University, Berlin, Germany) and RdRp-IP4 (RdRp, Institut Pasteur, Paris, France)) were selected and combined in a unique robust test; the resulting duo SARS-CoV-2 RT-qPCR assay was compared to the two parental monoplex tests. The duo SARS-CoV-2 assay performed equally, or better, in terms of sensitivity, specificity, linearity and signal intensity. We demonstrated that combining two single systems into a dual-target assay (with or without an MS2-based internal control) did not impair performances, providing a potent tool adapted for routine molecular diagnosis in clinical microbiology laboratories.